The aim of this project is to develop a model system for the study of several phases of sex hormone actions. The first phase is an investigation of the actio of progesterone at the subcellular level. Uteroglobin, a protein secreted by rabbit endometrium in response to progesterone and thought to be intimately associated with blastcyst development and implantation, is synthesized by rabbit endometrium in vitro. Studies are being conducted into various parameters affecting uteroglobin synthesis in order to gain some insight into the action ofprogesterone. Additionally, characterization of the RNA synthesized in response to progesterone is being carried out. Second, this in vitro response to progesterone will be used to investigate structure-activity relationships of the progesterone molecule using available synthetic progestogens. Species comparison of the activities of different progestogens will be carried out in order to find a model similar to man since haman endometrium is not readily availabe. Knowledge gained from these studies will be used to design specific progestogene and anti-progesterone for theraputic use.